1. Field of the Invention
The present invention relates to a heating and cooling roller, more particularly to a heating and cooling roller which cools a molten resin strip discharged from a die of an extruder or which heats a solidified resin strip.
2. Description of the Related Art
Heretofore, a heating and cooling roller is known which includes: a non-rotatably disposed inner cylinder; a rotatable outer cylinder disposed coaxially with the inner cylinder; an annular medium channel defined by a gap between an outer peripheral surface of the inner cylinder and an inner peripheral surface of the outer cylinder; slit-like medium inflow and outflow ports which are disposed in the inner cylinder and which extend along the approximately whole length of an axis of the inner cylinder; medium supply and discharge paths which are disposed in the inner cylinder to communicate with the medium inflow port and the medium outflow port, respectively, and which supply a medium to the medium inflow port or guide the medium from the medium outflow port to the outside; and a partition member which is disposed between the medium inflow port and the medium outflow port of the inner cylinder to divide the annular medium channel in a peripheral direction and which extends in an axial direction of the inner cylinder (see, e.g., Patent Document 1).
When the heating and cooling roller is used, a temperature distribution of the roller in a width direction can be constantly homogenized, because the slit-like medium inflow and outflow ports are extended along the approximately whole length of the axis of the fixed inner cylinder. This can reduce a lateral temperature fluctuation of a matter to be heated or cooled.
Moreover, since the medium inflow port is disposed in a fixed position, the matter to be heated or cooled first comes into contact with the outer peripheral surface of the outer cylinder constantly maintained at a predetermined temperature, and the matter moves with the rotation of the outer cylinder. Therefore, any temperature unevenness is not generated in a flow direction of the matter to be heated or cooled. Therefore, a flow rate of the medium does not affect the temperature evenness, and the flow rate of the medium can be reduced to reduce the vibrations of the roller and simplify a piping line. In addition, it is possible to control the temperature of the matter to be heated or cooled at the end of contact by controlling not only the medium temperature but also the medium flow rate.
Furthermore, since the medium is supplied from the fixed inner cylinder, there is produced an effect that any rotary joint does not have to be disposed in a medium supply portion.
[Patent Document 1] Japanese Patent Application Laid-Open No. 6-87150
Additionally, in the conventional cooling roller which cools the molten resin strip discharged from the die of the extruder, if a temperature difference can be achieved between a contact start point (the point where the molten resin strip discharged from the die of the extruder comes into contact with the cooling roller) on this cooling roller and a detached point (the point where the strip is detached from the cooling roller) on the cooling roller (outer surface of the outer cylinder), moldability of the molten resin strip is improved.
That is, a higher temperature of the cooling roller is preferred at the place where the molten resin strip discharged from the die comes into contact with the cooling roller. This is because there is improved a close contact property of the molten resin strip with the cooling roller, and there is reduced a temperature difference between a front and a back of the molten resin strip (sheet) in contact with the cooling roller.
On the other hand, a low temperature of the cooling roller is preferred at the detaching place where the resin strip cooled by the cooling roller departs from the cooling roller. This is because crystallization of the resin strip can be inhibited, and peelability of the resin strip from the cooling roller is improved.
However, in the conventional cooling roller, there exists only one medium channel formed by the gap between the outer peripheral surface of the inner cylinder and the inner peripheral surface of the outer cylinder. Therefore, there is a problem that it is not possible to individually control the temperature at the place where the molten resin strip discharged from the die comes into contact with the cooling roller, and the temperature at the parting place where the resin strip discharged from the die of the extruder departs from the cooling roller.
In other words, a conflicting state is caused in which when the temperature of the contact start place is raised, the temperature of the detaching place also rises. On the other hand, when the temperature of the detaching place is raised, the temperature of the contact start place drops. The temperature difference is caused only by the heat received from the molten resin strip. That means that an only small temperature difference (e.g., about 2° C. to 3° C.) is achieved between the temperature at the contact start place and the temperature at the detaching place, and it is difficult to obtain the above-described effects (the close contact property and an improved peelability of strip).
It is to be noted that the above problems arise not only in a case where the molten resin strip discharged from the die of the extruder is cooled but also in the heating roller which heats the solidified resin strip.